>Whether such practices are enforced overtly or through "incentives" is not a distinction that should automatically determine whether a regulator should take action or not.
It is, though, for the following reason:
"Incentive" implies some sort of trade-off (for example, Microsoft's bullying makes their software less useful and them less trustworthy, and they know they can only go so far before OEM's find it profitable to start selling no-OS or Linux systems).
It also requires the trade-off to be sustained for as long as Microsoft wants people to produce computers with their keys. So if Microsoft were to become a much smaller player in the market one day -- and looking at Windows 8, I expect this to happen soon -- they would be forced to stop pulling this crap.
To contrast, your example of us paying media companies for blank media, has none of the above. It was imposed by regulators (congress/parliament), working for a cabal of other regulators (RIAA/MPAA) with no trade-off, no choice, no accountability and no time limit. The fact is that the record companies would have failed years ago with such a poor business model, and the only reason they are alive today is because of regulatory capture.